‘The Cosmic Zoo – Complex Life on Many Worlds’ by Dirk Schulze-Makuch, William Bains

The key question in
astrobiology is whether we are likely to find life beyond Earth, and
the authors of this book, who are clearly optimistic about the
answer, put forward strong arguments to support their optimism.
Whether you agree with them or not, this book will help you think
critically about the possibility of life beyond Earth, and about the
likelihood of complex life being common in the universe, in direct
contrast to the Rare Earth hypothesis. It will also remind you of how
astonishing wonderful life on our planet is.

The
authors, Schulze-Makuch and Bains,
are scientists well-versed in microbiology, the chemistry and the
evolution of life. They start from the premise that if
abiogenesis is not particularly rare, simple life will appear in
other worlds as long as the conditions are right, and that complex
life will evolve as long as the environment remains habitable for
long enough. From here, they explore at length the different
bottlenecks that life on Earth had to go through in order to make the
jump from simple to complex life, and from complex life to
intelligent and technologically advanced societies. They provide an
extensive yet concise account of how life appears to have evolved on
Earth, and how different evolutionary pressures resulted in
increasing complexity of anatomy, physiology and behaviour. For each
key evolutionary step described, they ensure that the reader is aware
of the difficulties life had to overcome in order to make it through
a particular evolutionary barrier. However, they make a clear
distinction between processes that appear to be oddities and unlikely
to happen again, and processes that appear to be common and that have
occurred many times but in different ways. The authors’ focus is on
how likely it is that key evolutionary innovations will happen, even
if the path taken to get there is different from the one observed on
the Earth.

If life is
common in other worlds, and there are many ways for life to evolve
into complex organisms, then it is likely that we are living in a
cosmic zoo. However, as the authors point out towards the end of the
book, this is just a hypothesis, and one that cannot yet be tested.
Hopefully, the increasing pace of technological progress and our
continuous exploration of the Solar System will allow us to find some
answers in the not too distant future.

My only minor
criticism about this book is that I expected more discussion about
habitability and the extreme conditions under which life survives on
Earth, how this informs our search for life beyond Earth, and our
expectations of finding it.

I would highly
recommended The Cosmic Zoo to any undergraduate and postgraduate
student of Planetary Sciences and astrobiology; the further reading
lists provided at the end of each chapter are an added bonus. Because
the book is written in a jargon-free manner and has a helpful
glossary at the back, it is also a great read for anybody with an
interest in astrobiology, SETI, and the evolution of life on Earth.